The present invention relates generally to flight vehicles and more particularly to an inlet for a hypersonic flight vehicle engine.
At hypersonic Mach numbers (i.e., greater than Mach 5) a flight vehicle having an air breathing engine requires an engine inlet having a large air-capture region. In addition, hypersonic flight vehicle engine design requires inlet surfaces to be three-dimensionally-swept to reduce aerodynamic drag and friction heating. Three-dimensionally-swept engine inlet designs can produce non-planar flow components requiring a complex and perhaps impractical analysis of a three-dimensional airflow path. This may be contrasted with non-hypersonic supersonic engines having ramp inlet surfaces producing planar flow components allowing a much easier analysis of a two-dimensional airflow path. Furthermore, two-dimensional flow allows easier direct connect engine component testing (which means testing an engine component by duplicating its input conditions with some apparatus without having to use the upstream engine components to produce such input conditions), such as testing an engine without its large inlet by duplicating the two-dimensional airflow conditions calculated at the engine throat. Finally, a hypersonic engine design may introduce a pitch moment on the flight vehicle which would require a constant trim such as from a drag-producing control surface.
In describing the invention, the terminology "caret-shaped surface" will be used. For the purpose of this invention, a "caret-shaped surface" is defined as the surface of an isosceles triangle which has been folded along its base altitude line to form two mirror-image right triangles which meet along the altitude line with an anhedral angle. To help visualize this caret-shaped surface, one can cut an isosceles triangle out of a piece of stiff paper, and crease the triangle along the altitude line so that two mirror-image right triangles are superimposed on each other. (The steps up to now are identical to the beginning steps in making certain paper airplanes.) If the bent isosceles triangle is placed on the surface of a table, so that the legs of the isosceles triangle rest on the table surface, the two right triangle portions will form an anhedral angle at the altitude line. The lower (inside) surface of the bent isosceles triangle is a caret-shaped surface. The angle between the altitude line (the crease line) and the airflow is the angle of attack of the caret-shaped surface.
For unique combinations of hypersonic speed and angle of attack (hereinafter referred to as "predetermined operating conditions"), as can be determined by those skilled in the art, the above-defined caret-shaped surface will generate a plane shock wave in the plane of its leading edges (the plane containing the legs of the bent isosceles triangle which is also the plane of the table surface) which leads to a uniform pressure between the shock wave and the caret-shaped surface (the lower surface of the bent isosceles triangle) equal to the pressure behind the shock in a two-dimensional wedge flow. Two-dimensional wedge flow will be closely approximated for deviations from the design hypersonic speed and angle of attack.
The caret-shaped surface of the invention is the same as the lower surface of the caret wing of the literature. Caret wings are described in a paper by K. Kipke entitled "Experimental Investigations of Wave Riders in the Mach Number Range from 8 to 15 " published in AGARD Hypersonic Boundary Layers and Flow Fields (May, 1968), said paper hereby incorporated by reference.